A SnO2/MXene hybrid nanocomposite as a negative electrode material for asymmetric supercapacitors

Abstract

In this report, we synthesised a SnO₂/Ti₃C₂T_x composite through a single-step hydrothermal route with varying quantities of Ti₃C₂T_x (from 50 mg to 100 mg). The formation of a hybrid increases the interlayer spacing of Ti₃C₂T_x, and this increment in the interlayer spacing supports the charge transport in the electroactive material. Thus, the resultant composite with 80 mg of Ti₃C₂T_x (SnO₂/Ti₃C₂T_x-80) displays a specific capacitance of 620 F g⁻¹ at 2 A g⁻¹ current density. Density Functional Theory (DFT) calculations have been performed to comprehend the structural and electronic properties of SnO₂ and hybrid SnO₂/Ti₃C₂T_x systems. The formation of a hybrid structure has significantly increased the conductivity of the SnO₂ system due to the charge transfer from Ti₃C₂T_x to SnO₂. The quantum capacitance is higher in the hybrid system than in the pristine SnO₂ system. This validates and supports our experimental results that the hybrid system has enhanced charge storage performance. For practical realisation, an asymmetric supercapacitor (ASC) device is fabricated using SnO₂/Ti₃C₂T_x-80 as a negative electroactive material and cobalt phosphate as a positive electroactive material. The fabricated device delivers a specific capacitance of 100 F g⁻¹ at 3 A g⁻¹ current density. The ASC shows an energy density of 32 W h kg⁻¹ with a power density of 5118.5 W kg⁻¹. The device retains 93% of its initial capacitance even after 15 000 GCD cycles at 4.5 A g⁻¹ with a coulombic efficiency of 98%.